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一篇搞定Java序列化
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<ul>
<li><a href="#序列化">序列化</a></li>
<li><a href="#serializable">Serializable</a><ul>
<li><a href="#用法">用法</a></li>
<li><a href="#使用细节">使用细节</a></li>
</ul>
</li>
<li><a href="#parcelable">Parcelable</a><ul>
<li><a href="#特点">特点</a></li>
<li><a href="#用法-1">用法</a></li>
</ul>
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<li><a href="#xmlextensible-markup-language">XML（eXtensible Markup Language）</a><ul>
<li><a href="#特点-1">特点</a></li>
<li><a href="#用法-2">用法</a></li>
<li><a href="#使用细节-1">使用细节</a></li>
</ul>
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<li><a href="#jsonjavascript-object-notation">JSON（JavaScript Object Notation）</a><ul>
<li><a href="#特点-2">特点</a></li>
<li><a href="#fastjson-使用细节">fastjson 使用细节</a></li>
<li><a href="#各种json库的比较on-android">各种JSON库的比较（on Android）</a></li>
</ul>
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<li><a href="#protobufgoogle-protocol-buffers">Protobuf（Google Protocol Buffers）</a><ul>
<li><a href="#特点-3">特点</a></li>
<li><a href="#用法-3">用法</a><ul>
<li><a href="#写proto文件定义数据结构">写proto文件定义数据结构</a></li>
<li><a href="#生成java文件">生成java文件</a></li>
<li><a href="#导入jar包">导入jar包</a></li>
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<li><a href="#注意事项">注意事项</a></li>
<li><a href="#另一种选择">另一种选择</a></li>
</ul>
</li>
</ul>
<!-- tocstop -->
<h1 id="序列化"><a href="#序列化" class="headerlink" title="序列化"></a>序列化</h1><p>可以理解为一种数据对象和二进制串的转化协议，用于数据持久化和数据传输</p>
<h1 id="serializable"><a href="#Serializable" class="headerlink" title="Serializable"></a>Serializable</h1><h2 id="用法"><a href="#用法" class="headerlink" title="用法"></a>用法</h2><ol>
<li>数据对象实现java.io.Serializable，否则会抛出NotSerializableException</li>
<li>通过ObjectOutputStream和ObjectInputStream对对象进行序列化和反序列化</li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div></pre></td><td class="code"><pre><div class="line"><span class="meta">@Override</span></div><div class="line"><span class="keyword">public</span> <T> <span class="function"><span class="keyword">void</span> <span class="title">write</span><span class="params">(OutputStream output, T bean)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> ObjectOutputStream oos = <span class="keyword">null</span>;</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> oos = <span class="keyword">new</span> ObjectOutputStream(output);</div><div class="line"> oos.writeObject(bean);</div><div class="line"> } <span class="keyword">catch</span> (IOException e) {</div><div class="line"> e.printStackTrace();</div><div class="line"> } <span class="keyword">finally</span> {</div><div class="line"> IOUtils.closeQuietly(oos);</div><div class="line"> }</div><div class="line">}</div><div class="line"></div><div class="line"><span class="meta">@Override</span></div><div class="line"><span class="keyword">public</span> <T> <span class="function">T <span class="title">read</span><span class="params">(InputStream input, Class<T> entityClass)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> ObjectInputStream ois = <span class="keyword">null</span>;</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> ois = <span class="keyword">new</span> ObjectInputStream(input);</div><div class="line"> <span class="keyword">return</span> (T) ois.readObject();</div><div class="line"> } <span class="keyword">catch</span> (IOException | ClassNotFoundException e) {</div><div class="line"> e.printStackTrace();</div><div class="line"> <span class="keyword">return</span> <span class="keyword">null</span>;</div><div class="line"> } <span class="keyword">finally</span> {</div><div class="line"> IOUtils.closeQuietly(ois);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
<h2 id="使用细节"><a href="#使用细节" class="headerlink" title="使用细节"></a>使用细节</h2><ol>
<li>transient关键字修饰的变量，可以阻止序列化该变量。反序列化时，transient 变量会被赋值为初始值</li>
<li>在类中增加writeObject 和 readObject 方法可以实现自定义序列化策略<ul>
<li>ArrayList内部就是将元素transient了，然后自定义writeObject和readObject方法，因为ArrayList是动态数组，这样做可以避免大量空对象被序列化</li>
<li>加解密密数据可以在writeObject 和 readObject 中实现</li>
</ul>
</li>
<li>序列化不关注静态变量</li>
<li>父类不实现Serializable的话那么父类的变量不会被序列化</li>
<li>serialVersionUID一致时两个相同的类才能被序列化成功，没有特殊情况都用固定的1L即可<ul>
<li>特性案例：Server端重新生成serialVersionUID，可以导致Client端反序列化失败，强制客户端升级</li>
</ul>
</li>
<li><p>序列化会破坏单例模式</p>
<ul>
<li><p>要么用静态内部类的方式写单例</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Singleton</span> </span>{</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> <span class="class"><span class="keyword">class</span> <span class="title">Holder</span> </span>{</div><div class="line"> <span class="keyword">private</span> <span class="keyword">static</span> Singleton singleton = <span class="keyword">new</span> Singleton();</div><div class="line"> }</div><div class="line"> </div><div class="line"> <span class="function"><span class="keyword">private</span> <span class="title">Singleton</span><span class="params">()</span></span>{}</div><div class="line"> </div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Singleton <span class="title">getSingleton</span><span class="params">()</span></span>{</div><div class="line"> <span class="keyword">return</span> Holder.singleton;</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
</li>
<li><p>要么单例对象重写readReslove方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Singleton</span> <span class="keyword">implements</span> <span class="title">Serializable</span></span>{</div><div class="line"> <span class="keyword">private</span> <span class="keyword">volatile</span> <span class="keyword">static</span> Singleton singleton;</div><div class="line"> <span class="function"><span class="keyword">private</span> <span class="title">Singleton</span> <span class="params">()</span></span>{}</div><div class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> Singleton <span class="title">getSingleton</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">if</span> (singleton == <span class="keyword">null</span>) {</div><div class="line"> <span class="keyword">synchronized</span> (Singleton.class) {</div><div class="line"> <span class="keyword">if</span> (singleton == <span class="keyword">null</span>) {</div><div class="line"> singleton = <span class="keyword">new</span> Singleton();</div><div class="line"> }</div><div class="line"> }</div><div class="line"> }</div><div class="line"> <span class="keyword">return</span> singleton;</div><div class="line"> }</div><div class="line"> </div><div class="line"> <span class="function"><span class="keyword">private</span> Object <span class="title">readResolve</span><span class="params">()</span> </span>{</div><div class="line"> <span class="keyword">return</span> singleton;</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
</li>
</ul>
</li>
</ol>
<h1 id="parcelable"><a href="#Parcelable" class="headerlink" title="Parcelable"></a>Parcelable</h1><h2 id="特点"><a href="#特点" class="headerlink" title="特点"></a>特点</h2><p>Android特有，比Serializable高效，节省内存，可用于Intent传递和IPC，但不推荐用于持久化，因为存在版本差异</p>
<h2 id="用法"><a href="#用法-1" class="headerlink" title="用法"></a>用法</h2><ol>
<li>实现Parcelable</li>
<li>重写writeToParcel和Parcelable.Creator里的createFromParcel方法，注意顺序一定要一致</li>
</ol>
<h1 id="xmlextensible-markup-language"><a href="#XML（eXtensible-Markup-Language）" class="headerlink" title="XML（eXtensible Markup Language）"></a>XML（eXtensible Markup Language）</h1><h2 id="特点"><a href="#特点-1" class="headerlink" title="特点"></a>特点</h2><ol>
<li>XML被设计为传输和存储数据，W3C标准</li>
<li>具有自我描述性，但仅仅是纯文本，不会处理任何事情 </li>
</ol>
<h2 id="用法"><a href="#用法-2" class="headerlink" title="用法"></a>用法</h2><ol>
<li>基于事件驱动的SAX、Pull方式，内存占用少，使用比较复杂，还有把XML全部加载成树结构的DOM方式，使用灵活但内存占用多</li>
<li>我比较懒，直接用了Square Retrofit里的XML解析器-SimpleXML，使用就像JSON一样简单<figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">XmlConverter</span> <span class="keyword">implements</span> <span class="title">IConverter</span> </span>{</div><div class="line"> </div><div class="line"> <span class="keyword">private</span> <span class="keyword">final</span> Serializer serializer = <span class="keyword">new</span> Persister();</div><div class="line"> </div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="keyword">public</span> <T> <span class="function">String <span class="title">toString</span><span class="params">(T bean)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> ByteArrayOutputStream output = <span class="keyword">new</span> ByteArrayOutputStream();</div><div class="line"> write(output, bean);</div><div class="line"> <span class="keyword">return</span> output.toString();</div><div class="line"> }</div><div class="line"> </div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="keyword">public</span> <T> <span class="function">T <span class="title">toBean</span><span class="params">(String string, Class<T> entityClass)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> <span class="keyword">if</span> (entityClass == String.class</div><div class="line"> || entityClass == CharSequence.class){</div><div class="line"> <span class="keyword">return</span> (T)string;</div><div class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (entityClass == <span class="keyword">char</span>[].class){</div><div class="line"> <span class="keyword">return</span> (T)string.toCharArray();</div><div class="line"> } <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">return</span> serializer.read(entityClass, string);</div><div class="line"> }</div><div class="line"> }</div><div class="line"> </div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="keyword">public</span> <T> <span class="function"><span class="keyword">void</span> <span class="title">write</span><span class="params">(OutputStream output, T bean)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> serializer.write(bean, output);</div><div class="line"> }</div><div class="line"> </div><div class="line"> <span class="meta">@Override</span></div><div class="line"> <span class="keyword">public</span> <T> <span class="function">T <span class="title">read</span><span class="params">(InputStream input, Class<T> entityClass)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> <span class="keyword">return</span> serializer.read(entityClass, input);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure>
</li>
</ol>
<h2 id="使用细节"><a href="#使用细节-1" class="headerlink" title="使用细节"></a>使用细节</h2><p>某些文本，比如 JavaScript 代码，包含大量 “<” 或 “&” 字符。为了避免错误，可以将脚本代码定义为 CDATA。CDATA 部分中的所有内容都会被解析器忽略。<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div></pre></td><td class="code"><pre><div class="line">//CDATA 由 <![CDATA[ 开始，由 ]]> 结束</div><div class="line">//以下五种符号需要做转义</div><div class="line">&lt; < 小于</div><div class="line">&gt; > 大于</div><div class="line">&amp; & 和号</div><div class="line">&apos; ' 省略号</div><div class="line">&quot; " 引号</div></pre></td></tr></table></figure></p>
<h1 id="jsonjavascript-object-notation"><a href="#JSON（JavaScript-Object-Notation）" class="headerlink" title="JSON（JavaScript Object Notation）"></a>JSON（JavaScript Object Notation）</h1><h2 id="特点"><a href="#特点-2" class="headerlink" title="特点"></a>特点</h2><ol>
<li>用“属性-值”的方式来描述对象，保持了人眼可读的优点</li>
<li>相比XML数据更加简洁(文件大小将近一半)，解析更快</li>
<li>JS的先天支持，广泛应用于web browser场景中，有良好的扩展性和兼容性</li>
</ol>
<h2 id="fastjson-使用细节"><a href="#fastjson-使用细节" class="headerlink" title="fastjson 使用细节"></a>fastjson 使用细节</h2><ol>
<li>要有默认构造方法，或者有@JSONCreator的构造方法，不然会报JSONException</li>
<li>要有成员要public或者要有get/set方法(我们工程约定统一用get/set方法)，不然解析不到</li>
<li>用@JSONField(name=”xxx”)指定key名字，不指定的话采用变量名，可能会被代码混淆导致解析错误</li>
<li>用@JSONField(format=”yyyyMMdd”)配置日期格式</li>
<li>有些场景属性互相依赖，需要在构造方法中做初始化，可以使用@JSONCreator来指定构造函数<ul>
<li>@JSONCreator只能有一个</li>
<li>参数必须添加注解@JSONField(name=”xxx”)</li>
<li>子类的@JSONCreator不会继承父类的@JSONCreator</li>
</ul>
</li>
<li>有些场景属性相互依赖，需要在bean反序列化后对数据做二次处理，可以使类实现JavaBeanDeserializerListener，在onDeserializerSuccess做二次处理</li>
<li>序列化默认跳过null，如果需要序列化，可以再序列化方法里传SerializerFeature WriteMapNullValue：是否输出值为null的字段,默认为false<br>还有其他feature：<ul>
<li>QuoteFieldNames 输出key时是否使用双引号,默认为true </li>
<li>WriteNullNumberAsZero 数值字段如果为null,输出为0,而非null </li>
<li>WriteNullListAsEmpty List字段如果为null,输出为[],而非null </li>
<li>WriteNullStringAsEmpty 字符类型字段如果为null,输出为””,而非null </li>
<li>WriteNullBooleanAsFalse Boolean字段如果为null,输出为false,而非null </li>
</ul>
</li>
<li>顺序问题<ul>
<li>数组和List不会乱序</li>
<li>在1.1.26版本 JSONObject和Bean序列化后会乱序，</li>
<li>在1.1.41会按key的顺序重新排序，</li>
<li>在1.1.42之后可以通过@JSONField(ordinal = 1)指定顺序</li>
<li>还可以在类上配置@JSONType(orders = {})来设置顺序</li>
</ul>
</li>
<li>反序列化遇到重复的key，以后面的为准</li>
</ol>
<h2 id="各种json库的比较on-android"><a href="#各种JSON库的比较（on-Android）" class="headerlink" title="各种JSON库的比较（on Android）"></a>各种JSON库的比较（on Android）</h2><ul>
<li>依赖比较： fastjson(202K) < gson(226K) < jackson(33+190+828=1051K)</li>
<li>流行度： gson > fastjson > jackson //p.s. fastjson仅在中国流行</li>
<li>速度比较：小数据量上fastjson和gson差不多，优于jackson；大数据量上，fastjson和jackson差不多，gson很差<ul>
<li>p.s. fastjson在jvm平台上的性能比在Android上优秀，因为运用了ASM库</li>
</ul>
</li>
<li>用法比较：<ul>
<li>fastjson：<ol>
<li>对构造方法、get/set方法的规范比较多（见上文），不留神容易遇到坑</li>
<li>旧版本bug比较多，最好使用最新版 </li>
</ol>
</li>
<li>gson：<ol>
<li>类型不对不报错，直接返回默认值</li>
<li>默认不序列化null，如果需要序列化：Gson gson = new GsonBuilder().serializeNulls().create(); </li>
<li>如果需要反序列化null为””，需要注册TypeAdapter，如果需要反序列化null为空list，需要添加@JsonAdapter注解(可参考我针对这个写的一篇<a href="http://blog.csdn.net/efan006/article/details/50544509" target="_blank" rel="external">博客日志</a>)</li>
</ol>
</li>
<li>jackson：序列化默认不会跳过null，如果需要跳过<ul>
<li>可以在数据对象上使用@JsonInclude(Include.NON_NULL)</li>
<li>也可以在序列化方法上mapper.setSerializationInclusion(Include.NON_NULL); </li>
</ul>
</li>
</ul>
</li>
</ul>
<h1 id="protobufgoogle-protocol-buffers"><a href="#Protobuf（Google-Protocol-Buffers）" class="headerlink" title="Protobuf（Google Protocol Buffers）"></a>Protobuf（Google Protocol Buffers）</h1><h2 id="特点"><a href="#特点-3" class="headerlink" title="特点"></a>特点</h2><ol>
<li>Google开发的一种轻便高效的数据存储格式, 适合内部对性能要求高的RPC调用</li>
<li>特点是二进制格式，数据量小（相当于json的40%左右），解包速度快，非常适合数据存储或交换</li>
<li>proto2仅支持Java，C++，Python三种语言, proto3还支持JavaScript, Objective-C, Ruby, C#, Go.</li>
</ol>
<h2 id="用法"><a href="#用法-3" class="headerlink" title="用法"></a>用法</h2><h3 id="写proto文件定义数据结构"><a href="#写proto文件定义数据结构" class="headerlink" title="写proto文件定义数据结构"></a>写proto文件定义数据结构</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div></pre></td><td class="code"><pre><div class="line">//可以写注释，会自动转到java类里</div><div class="line"></div><div class="line">import "xxx.proto" //import表示依赖其他proto文件</div><div class="line">option java_package = "com.fs.fsprobuf"; //java_package 代表这个文件所在的包名</div><div class="line">option java_outer_classname = "User"; //java_outer_classname 即为类名</div><div class="line"></div><div class="line">message Person { //message代表一个类</div><div class="line"> </div><div class="line"> enum PhoneType{ //enum是一个枚举类型</div><div class="line"> MOBILE = 0; </div><div class="line"> HOME = 1;</div><div class="line"> WORK = 2;</div><div class="line"> }</div><div class="line"></div><div class="line"> message PhoneNumber{</div><div class="line"> required string number = 1; //required 代表该字段必填，没传值会报错</div><div class="line"> optional PhoneType type = 2[default = HOME] //optional 代表该字段可选，并可以为其设置默认值，默认值格式[defalut=]。</div><div class="line"> }</div><div class="line"></div><div class="line"> required int32 id = 2; //整型int32 布尔值bool</div><div class="line"> required string name = 1; //required int32 userId = 1 (修饰词 类型 域名 = 标记值)这是一个域 </div><div class="line"> optional string email = 3[default="123"]; //标记值是用来在二进制编码里唯一确认当前域的</div><div class="line"> repeated PhoneNumber phone = 4; //repeated 代表一个list</div><div class="line">}</div></pre></td></tr></table></figure>
<h3 id="生成java文件"><a href="#生成java文件" class="headerlink" title="生成java文件"></a>生成java文件</h3><p>使用官方工具把proto文件编译成java文件，放到工程里与package对应的路径下<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">protoc-java.exe --java_out=./ *.proto</div></pre></td></tr></table></figure></p>
<h3 id="导入jar包"><a href="#导入jar包" class="headerlink" title="导入jar包"></a>导入jar包</h3><p>下载官方的protobuf-java的jar包引入到工程里，使用工具类进行数据读写<br><figure class="highlight java"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div></pre></td><td class="code"><pre><div class="line"><span class="meta">@overide</span></div><div class="line"><span class="keyword">public</span> <T> <span class="function"><span class="keyword">void</span> <span class="title">write</span><span class="params">(OutputStream output, T bean)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> <span class="keyword">if</span> (bean <span class="keyword">instanceof</span> MessageLite){</div><div class="line"> ((MessageLite)bean).writeTo(output);</div><div class="line"> } <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(bean.getClass().getName() + <span class="string">"is not a protobuf message"</span>);</div><div class="line"> }</div><div class="line">}</div><div class="line"></div><div class="line"><span class="meta">@overide</span></div><div class="line"><span class="keyword">public</span> <T> <span class="function">T <span class="title">read</span><span class="params">(InputStream input, Class<T> entityClass)</span> <span class="keyword">throws</span> Exception </span>{</div><div class="line"> <span class="keyword">if</span> (MessageLite.class.isAssignableFrom(entityClass)) {</div><div class="line"> Parser<MessageLite> parser;</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> Field field = entityClass.getDeclaredField(<span class="string">"PARSER"</span>);</div><div class="line"> parser = (Parser<MessageLite>) field.get(<span class="keyword">null</span>);</div><div class="line"> <span class="keyword">return</span> (T)parser.parseFrom(input);</div><div class="line"> } <span class="keyword">catch</span> (NoSuchFieldException | IllegalAccessException e) {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(</div><div class="line"> <span class="string">"Found a protobuf message but "</span> + entityClass.getName() + <span class="string">" had no PARSER field."</span>);</div><div class="line"> }</div><div class="line"> } <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(entityClass.getName() + <span class="string">"is not a protobuf message"</span>);</div><div class="line"> }</div><div class="line">}</div></pre></td></tr></table></figure></p>
<h2 id="注意事项"><a href="#注意事项" class="headerlink" title="注意事项"></a>注意事项</h2><ol>
<li>升级proto定义，不可修改现有域的标记值，不可添加/删除required域。可以删除optional，repeated域。添加optional，repeated域必须采用不同的标记值（之前删除过的也不能用）</li>
<li>proto文件转成的java类 带有大量的方法(实测仅3个变量的类，生成了近100个方法，800行代码)。这在Android上极易导致方法数超65535上限</li>
</ol>
<h2 id="另一种选择"><a href="#另一种选择" class="headerlink" title="另一种选择"></a>另一种选择</h2><p>我们也可以采用Square Wire 项目的proto工具 </p>
<ol>
<li>首先也是写proto文件，一样的 </li>
<li>在项目gradle里引入wire组件<figure class="highlight gradle"><table><tr><td class="gutter"><pre><div class="line">1</div><div class="line">2</div><div class="line">3</div><div class="line">4</div><div class="line">5</div><div class="line">6</div><div class="line">7</div><div class="line">8</div><div class="line">9</div><div class="line">10</div><div class="line">11</div><div class="line">12</div><div class="line">13</div><div class="line">14</div><div class="line">15</div><div class="line">16</div><div class="line">17</div><div class="line">18</div><div class="line">19</div><div class="line">20</div><div class="line">21</div><div class="line">22</div><div class="line">23</div><div class="line">24</div><div class="line">25</div><div class="line">26</div><div class="line">27</div><div class="line">28</div><div class="line">29</div><div class="line">30</div><div class="line">31</div><div class="line">32</div><div class="line">33</div><div class="line">34</div></pre></td><td class="code"><pre><div class="line"><span class="keyword">compile</span> <span class="string">'com.squareup.wire:wire-runtime:2.2.0'</span> </div><div class="line">``` </div><div class="line"><span class="number">3</span>. 然后下载wire-compiler-VERSION-jar-with-<span class="keyword">dependencies</span>.jar工具，这个需要去maven仓库下载[下载地址](http:<span class="comment">//search.maven.org/#search|ga|1|g%3A%22com.squareup.wire%22) 注意要选择与gradle引入的wire版本一致</span></div><div class="line"><span class="number">4</span>. 使用cmd执行命令生成java文件 </div><div class="line">``` </div><div class="line">java -jar -Dfile.encoding=UTF-<span class="number">8</span> wire-compiler-<span class="number">2.2</span>.<span class="number">0</span>-jar-with-<span class="keyword">dependencies</span>.jar --proto_path=. --java_out=. *.proto </div><div class="line">``` </div><div class="line"><span class="number">5</span>. 使用工具类读写</div><div class="line">``` java</div><div class="line"> @Override</div><div class="line"> <span class="keyword">public</span> <T> <span class="keyword">void</span> <span class="keyword">write</span>(OutputStream output, T bean) <span class="keyword">throws</span> Exception {</div><div class="line"> <span class="keyword">if</span> (bean <span class="keyword">instanceof</span> Message){</div><div class="line"> ((Message)bean).encode(output);</div><div class="line"> } <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(bean.getClass().getName() + <span class="string">" is not a protobuf message"</span>);</div><div class="line"> }</div><div class="line"> }</div><div class="line"> </div><div class="line"> @Override</div><div class="line"> <span class="keyword">public</span> <T> T <span class="keyword">read</span>(InputStream input, <span class="keyword">Class</span><T> entityClass) <span class="keyword">throws</span> Exception {</div><div class="line"> <span class="keyword">if</span> (Message.<span class="keyword">class</span>.isAssignableFrom(entityClass)) {</div><div class="line"> ProtoAdapter<Message> adapter;</div><div class="line"> <span class="keyword">try</span> {</div><div class="line"> Field field = entityClass.getDeclaredField(<span class="string">"ADAPTER"</span>);</div><div class="line"> adapter = (ProtoAdapter<Message>)field.get(<span class="keyword">null</span>);</div><div class="line"> <span class="keyword">return</span> (T)adapter.decode(input);</div><div class="line"> } <span class="keyword">catch</span> (NoSuchFieldException | IllegalAccessException e) {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(</div><div class="line"> <span class="string">"Found a protobuf message but "</span> + entityClass.getName() + <span class="string">" had no ADAPTER field."</span>);</div><div class="line"> }</div><div class="line"> } <span class="keyword">else</span> {</div><div class="line"> <span class="keyword">throw</span> <span class="keyword">new</span> IllegalArgumentException(entityClass.getName() + <span class="string">" is not a protobuf message"</span>);</div><div class="line"> }</div><div class="line"> }</div></pre></td></tr></table></figure>
</li>
</ol>
<p>使用wire项目的工具，方法数显著裁剪了（还是之前3个变量的类，方法20多个，188行代码）</p>
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<time title="Post created" itemprop="dateCreated datePublished" datetime="2016-11-23T15:06:07+08:00">
2016-11-23
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<p>Welcome to <a href="https://hexo.io/" target="_blank" rel="external">Hexo</a>! This is your very first post. Check <a href="https://hexo.io/docs/" target="_blank" rel="external">documentation</a> for more info. If you get any problems when using Hexo, you can find the answer in <a href="https://hexo.io/docs/troubleshooting.html" target="_blank" rel="external">troubleshooting</a> or you can ask me on <a href="https://github.com/hexojs/hexo/issues" target="_blank" rel="external">GitHub</a>.</p>
<h2 id="quick-start"><a href="#Quick-Start" class="headerlink" title="Quick Start"></a>Quick Start</h2><h3 id="create-a-new-post"><a href="#Create-a-new-post" class="headerlink" title="Create a new post"></a>Create a new post</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo new <span class="string">"My New Post"</span></div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/writing.html" target="_blank" rel="external">Writing</a></p>
<h3 id="run-server"><a href="#Run-server" class="headerlink" title="Run server"></a>Run server</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo server</div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/server.html" target="_blank" rel="external">Server</a></p>
<h3 id="generate-static-files"><a href="#Generate-static-files" class="headerlink" title="Generate static files"></a>Generate static files</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo generate</div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/generating.html" target="_blank" rel="external">Generating</a></p>
<h3 id="deploy-to-remote-sites"><a href="#Deploy-to-remote-sites" class="headerlink" title="Deploy to remote sites"></a>Deploy to remote sites</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><div class="line">1</div></pre></td><td class="code"><pre><div class="line">$ hexo deploy</div></pre></td></tr></table></figure>
<p>More info: <a href="https://hexo.io/docs/deployment.html" target="_blank" rel="external">Deployment</a></p>
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